Recent years have seen advances in the development of technologies for purifying soil, groundwater and the like contaminated with organic halogenated compounds, by decomposing the compounds so as to reduce the contamination level. This development is directed basically to obtaining decomposers with high capability to decompose the organic halogenated compounds constituting the contaminants. Iron powder is a typical decomposer. For example, Patent Document 1 teaches that soil contaminated with an organic halogenated compound like trichloroethylene can be effectively treated to decompose the trichloroethylene or the like in the soil by mixing therein iron powder containing 0.1 wt % or more of C (carbon) and having a specific surface area of 500 cm2/g or greater.
Patent Document 2 teaches that high-purity iron powder containing C: less than 0.1 mass %, Si: less than 0.25 mass %, Mn: less than 0.60 mass %, P: less than 0.03 mass %, S: less than 0.03 mass % and O: less than 0.5 mass % is effective for purifying soil or water contaminated with a recalcitrant organic halogenated compound like 1,2-cis-dichloroethylene (cis-1,2-DCE).
However, a need was felt for a decomposer with even stronger decomposition capability. To meet this need, Patent Document 3, Patent Document 4 and Patent Document 5, which are in the name of the same applicant as the applicant of this application, propose copper-containing iron powders obtained by depositing metallic copper on the surfaces of iron powder particles. When such a copper-containing iron powder is added to and mixed with soil, groundwater or the like contaminated with an organic halogenated compound, the organic halogenated compound is efficiently decomposed. Nevertheless, a decomposer with even higher decomposition is desired.
Patent Document 1: JP 11-235577A
Patent Document 2: JP 2002-316050A
Patent Document 3: JP 2000-005740A
Patent Document 4: JP 2002-069425A
Patent Document 5: JP 2003-339902A